1. Field of the Invention
The present invention relates to a conductor paste for producing internal conductor layers of a small-size, a light-weight ceramic multilayer structure such as a ceramic multilayer wiring substrate or a laminated ceramic capacitor, and a method of manufacturing the ceramic multilayer structure using the conductor paste.
2. Description of the Prior Art
Conventionally, for the conductor paste metal used for producing the internal conductor of the ceramic multilayer structure, noble metals, such as Pt, Pd, Au and Ag and alloys thereof, have widely been used. The noble metal paste can be fired in air, but has a disadvantage that it is expensive.
Recently, there has been developed a method of using base metal, such as Ni or Cu. Ni or Cu is not only inexpensive but also superior in migration, especially Cu is highly conductive. Such method of using the base metal is disclosed in, for example, U.S. Pat. Nos 4,172,919 and 4,323,483.
The method of using the base metal has a problem that the firing condition is complicated. The base metal like Cu will be oxidized unless fired in an inert atmosphere such as nitrogen atmosphere. On the other hand, since the multilayer material contains a large quantity of organic binder, oxygen is needed to decompose and remove the organic binder. Unless the binder is sufficiently removed, it remains as carbon, which adversely affects the dielectric property. Hence, an atmosphere compatible with both removal of organic binder and prevention of oxidation of metal must be kept during the firing. Considering the complicated control of atmosphere during the firing, this method is not suitable to mass-production.
We have developed a new method in which the base metal, such as Cu or Ni, is used in the form of oxide so that the organic binder is removable in air. This method comprises producing a multilayer of dielectric paste and conductor paste mainly composed of CuO or NiO, removing the organic binder, in air reducing the oxide in N.sub.2 +H.sub.2 atmosphere, and firing the product in N.sub.2 atmosphere. This method is disclosed in U.S. Pat. No. 4,714,570. A further improved CuO paste is disclosed in U.S. Pat. No. 4,695,403.
This method has facilitated atmospheric control during the firing, but has a point yet to be improved. Since base metal is used as oxide, shrinkage of volume of the internal conductor occurs during the reduction, thereby degrading the uniformity of the conductor layers. It is considered that the conductor layer may be made thick. But, this is not suitable to the case of a small-size, large capacitance laminated capacitor. In other words, it is required for increasing capacity per unit volume to reduce both the thickness of the conductor layer and the thickness of the dielectric layer.